2. Field of Invention
This invention relates to a sizing agent for materials composed of glass, such as glass fibers. More particularly, the sizing agent provided by the present invention is characterized in that a bisphenol type self-emulsifiable polyester modified with an amino glycol is used as a film-forming substance. When the sizing agent of the present invention is employed, undesired green or greenish brown discoloration in the appearance of a glass fiber-reinforced article can be effectively prevented.
2. Description of Invention
For curing of unsaturated polyester resin, there are generally employed a hydroperoxide, an acyl peroxide, a ketone peroxide or the like as a catalyst and a cobalt salt as a curing accelerator, and this curing technique is applied to production of glass fiber-reinforced articles (FRP). However, when an unsaturated polyester is cured according to such curing method, in the resulting reinforced article an undesired green or greenish brown discoloration is often observed to degrade the appearance characteristics. Since these glass fiber reinforced plastics are recently applied vigorously to production of furnitures, decorative laminates and the like, this green or greenish brown discoloration is now more undesired. Especially when a bisphenol type unsaturated polyester is used as a matrix resin, since a tertiary amine is used as a curing accelerator, discoloration is readily caused in the cured product even by slight changes in curing conditions. This undesired phenomenon of discoloration is caused by complicated influences of the exothermic temperature at the curing step, the cobalt content, the ambient temperature at the molding step, the kind and amount of the glass fiber-treating agent and other factors, and it is very difficult to elucidate causes of the discoloration.